Our society generates a tremendous amount of hydrocarbon and carbohydrate-based waste. Some wastes are easily segregated and recycled, while others are not. A variety of waste based on available technology cannot be economically recycled into a usable, saleable, clean, high BTU content gas.
The United States generates over 200,000,000 tons per year of municipal solid waste (MSW). This waste contains many different types of carboneous materials like hydrocarbon based, carbohydrate and cellulose-based materials.
MSW typically contains on a dry basis the following percentage of components:
______________________________________ Volatile Matter 79.56% Fixed Carbon 9.98% Ash 20.46% C 45.52% H 5.75% N 0.29% O 37.79% S 0.19% ______________________________________ EQU Cl 0.43-1.54%
Some municipalities have installed plants that separate the burnable fraction from metals and other non-burnables. The burnable material is commonly called Refuse Derived Fuel (RDF). It contains leather, rubber, plastics, paper, yard waste, etc.
The United States scraps about 10,000,000 automobiles per year. A large portion of the automobiles are shredded. After shredding, the non-metal portion is separated from the metallics in air classifiers or like means. Such material is commonly called "fluff" or Automobile Shredder Residue (ASR). Such material is light and fluffy. Over 1.5 million tons of ASR per year are generated. Currently, ASR is being land filled, using up very valuable space.
It is almost impossible to economically separate the plastics using solvent extraction or other chemical or mechanical methods from the fluff. The fluff normally includes polyurethanes, leather, vinyls, glass, nylons and other thermal and heat-setting plastics.
Automobile and truck tires continue to be a disposal problem throughout the United States. In addition to the 200 million tires discarded in this country every year, there exist another one billion tires in piles.
The steel industry uses large quantities of oil in the production of sheet and strip steel products. A large percentage of rolling oils, lubricating oils, and hydraulic oils eventually are removed in the waste water treatment plant in the form of a high oil content sludge. A typical large, integrated steel mill generates between 50,000 and 100,000 tons per year. The major steel industry mills have an on-site plant to treat and separate their waste water coming from the finishing part of the mill. The sludge typically contains:
______________________________________ Oil 5-15% Dry Basis Solids 95-85% Dry Basis Water 30-60% ______________________________________
Such oil containing sludge is stockpiled openly to the atmosphere such that acid rain leaches out the oil and other heavy metals. A typical steel mill may stockpile between 300,000 to 800,000 tons of the waste water treatment plant sludge.
Some of the oil from the rolling operation in a typical steel mill ends up in mill scale. Mill scale is also stockpiled outside where the oil may leach into the ground. Mill scale typically contains:
______________________________________ Oil 1-15% Iron Oxide 60-75% ______________________________________
One U.S. mill is currently trying a detergent process to wash out the oil. The oily wash water goes to the waste water treatment plant, where some of the oil accumulates in the sludge.
Over the past several decades, there have been attempts to volatize hydrocarbons from such solid waste. Such processes have included indirect retort processes. Heat Carrier Solids (HCS) have been used to remove hydrocarbons from solids. In the 1970's, Tosco used aluminum oxide balls to recover oil from oil shale.
U.S. Pat. No. 3,008,894 issued Nov. 14, 1961 to W. J. Culbertson, Jr. is exemplary of oil recovery from oil shale.
Similar processes use fine particle HCS to recover oil from oil-bearing solids. In these processes, the objective is to produce a distillate liquid that can either become feed stock for an oil refinery or other oil-based product.
Another method employed in the past for heating solids indirectly is through a metallic or ceramic shell, such as an indirectly-fired heated retort. A limitation to this approach is the amount of heat that can be transferred through the thickness of the metallic or ceramic shell.
More recently, Battelle of Columbus, Ohio has effected gasification of wood chips and RDF in a biomass gasification process, producing medium-BTU product gas. U.S. Pat. No. 4,828,581 exemplifies the Battelle approach, utilizing two circulating fluid bed reactors, one of which is a gasification reactor in which the biomass is converted into a medium BTU gas and residual char, and a second, is a combustion reactor that burns the residual char to provide heat for the direct gasification of the biomass. Heat transfer between the reactors is accomplished by circulating sand (HCS) between the gasifier and the combustor.
While the Battelle process effects direct gasification of wood chips and RDF, such process and apparatus requires the use of steam or nitrogen to maintain two fluidized beds, increasing the process cost by the fluidization, while additionally requiring extraneous energy and extraneous fluid to support the particles in the fluidizing bed reactors. The energy cost of the system is quite high, and the fluidized bed combustor also requires a source of compressed air, both of which may not be readily available on the situs of the gasification apparatus.
It therefore a primary object of this invention to provide an indirect retort process for treatment of shredded MSW and like waste, with increased thermal efficiency in an apparatus and process which is highly simple, and which is applicable for direct gas conversion of a variety of hydrocarbon content waste that to date cannot either be technically or economically recycled into a usable, saleable clean and high BTU content gas.
It is a further object of this invention to provide a method and apparatus for the direct gasification of municipal and like waste, which automatically removes acids and particulates from materials in the gas phase, which eliminates the need for fluidized beds or like lifting devices in the direct gasification of the waste, and in heating the Heat Carrying Solids (HCS) prior to contact with the treatable waste.
These and other objects of the present invention will be more clearly understood by reference to the following description and to the accompanying drawings.